A conventional vehicle air conditioning unit, for example, is described in JP-A-H8-48128. As shown in FIG. 4, this vehicle air conditioning unit has a duct 100, through which air is introduced into inside of a vehicle. The duct 100 is partitioned in its inside by a partition board 110 into a driver side air passage 120 and a front passenger side air passage 130. Moreover, air mix doors (not shown) are provided for the respective air passages 120, 130. The respective air mix doors are separately controlled, thereby being capable of separately controlling the respective temperatures in the air passages 120, 130. Moreover, the vehicle air conditioning unit has FACE air outlets 170, respectively formed in the air passages 120, 130, FOOT air outlets 160, respectively formed in the air passages 120, 130, and an air outlet switching door (not shown) for switching the openings of the air outlets 170, 160. The air outlet switching door is provided only one and commonly used for the air passages 120, 130. Therefore, an actuator 140 for driving the air outlet switching door is disposed on one side of the duct 100.
Recently, a vehicle air conditioning unit, particularly, a rear air conditioning unit is required to be downsized in order to enlarge the passenger compartment of a vehicle. For example, a structure shown in FIG. 5 is employed, in which a recess 150 is formed in a side part of the duct 100 and the actuator 140 is disposed in the recess 150. Accordingly, this air conditioning unit is more compact than that shown in FIG. 4, and thereby the passenger compartment can be downsized.
However, the above vehicle air conditioning units, which can separately control the temperatures in the respective air passages 120, 130, are suitable to employ a symmetrical duct shape for preserving the balance between the temperatures and between the amounts of the blowing air in the respective air passages 120, 130. In the vehicle air conditioning unit shown in FIG. 4, the recess 150 is formed in the side part of the duct 100, thereby making the corresponding cross-sectional areas of the left and right side air passages 120, 130 different. Therefore, the amounts of air blowing in the left side air passage 120 and in the right side air passage 130 are unbalanced, and thereby the temperature control performance is disadvantageously lowered.